In the prior art, a wide range of treatment methods having the purpose of refraction correction in the human eye are known. In this context, the purpose of the operation methods is to alter the cornea selectively so as to influence the light refraction in the eye. A plurality of operation methods are used for this purpose. At present, what is known as laser-assisted in situ keratomileusis, also known as LASIK for short, is the most widespread. In this context, a cornea lamella is initially detached from the cornea surface on one side and folded to the side. This lamella can be detached by means of a mechanical microkeratome, or also by means of what is known as a laser keratome, such as is marketed for example by Intralase Corp., Irvine, USA. After the lamella has been detached and folded to the side, the LASIK operation provides the use of an excimer laser, which removes, by ablation, the corneal tissue which is exposed under the lamella in this manner. After the volume present under the cornea surface has been vaporised in this manner, the cornea lamella is folded back onto the original spot again.
The use of a laser keratome to expose the lamella is advantageous compared to a mechanical blade, since the geometric precision is improved and the frequency of clinically significant complications is reduced. In particular, the lamella can be produced with a much more constant thickness if laser radiation is used. The cut edge is also precisely formed, and this reduces the risk of healing difficulties as a result of this boundary surface which remains even after the operation. However, a drawback of this method is that two different treatment devices have to be used, specifically on the one hand the laser keratome for exposing the lamella and on the other hand the laser which vaporises the corneal tissue.
These drawbacks are eliminated in a method which was implemented very recently by Carl Zeiss Meditec. In this lenticule extraction method, a cutting geometry which separates a cornea volume (known as a lenticule) in the cornea is formed in the cornea of the eye by means of a short-pulse laser, preferably a femtosecond laser. This is then removed manually by the operator. One advantage of this method is that the cutting quality is further improved by the use of the femtosecond laser.
Moreover, only one treatment device is now necessary; the excimer laser is no longer used.
A development of the method is referred to in the literature as the SMILE method, in which instead of producing a flap, merely a small opening cut provides access to the lenticule positioned under what is known as the cap. The separated lenticule is removed through this small opening cut, damaging the biomechanical integrity of the anterior cornea less than in LASIK, FLEX or PRK. In addition, fewer nerve fibres in the cornea are cut up in this manner, and this has a demonstrably favourable effect on the restoration of the original sensitivity of the cornea surface. The symptom of dry eyes, which often has to be treated after LASIK, is thus reduced in intensity and duration. Other complications following LASIK, which generally relate to the flap (for example folding, epithelial ingrowth in the flap bed), occur more rarely with no flap.
When producing cutting surfaces in the cornea by means of laser radiation, the optical radiation effect is usually exploited in that an optical aperture is produced by means of individual optical pulses, the duration of which may be between 100 fs and 100 ns. It is also known to introduce individual pulses, the energy of which is below a threshold for an optical aperture, into the tissue or material with an overlap, in such a way that material or tissue separation is achieved in this way too. This idea for producing a cut in the corneal tissue makes a large number of cuts possible.
It is also part of the prior art to increase the depth of field of a human eye in order to overcome the loss of accommodation of age-related farsightedness (presbyopia) (compensation for presbyopia). Another possibility consists in introducing an implant (also known as an inlay) into the cornea of at least one eye of an affected patient. In this case, the implant can be of an artificial nature, e.g. a ring or lens made of a plastics material (e.g. KAMRA®,)Flexivue®, or a correspondingly shaped implant made of a biomaterial or a transplant made of human corneal tissue.
It is also conventional for the currently available implants to produce a pocket-like cutting geometry in the cornea by means of a femtosecond laser keratome, which cutting geometry is determined for receiving the implant and simultaneously facilitates the introduction of the implant by the doctor.
In this case, it is helpful for the affected eye to have a far point in the range of between 0.3 m and infinity. If this is not the case, the refractive power of the eye must additionally be corrected by means of an optical aid (glasses or contact lenses). It is already possible to use surgical correction methods (PRK or LASIK using an excimer laser) to refractively correct affected eyes again before or after implanting an inlay (post-correction).
If the correction takes place after implanting an inlay, the interaction between the treatment method and the inlay poses a largely incalculable risk to the efficacy and safety of the method overall.
If the correction takes place before implanting an inlay, the conditions created by the previous refractive correction are not suitable for ensuring optimal implantation. In this case, there is therefore great potential for improving the efficacy and safety of the overall method of the compensation for presbyopia.
As lenticular extraction methods, the methods consolidated under the trade names ReLEx®, namely ReLEx® flex and ReLEx® smile of the company Carl Zeiss Meditec, are both fundamentally suitable for being combined with an implantation method in which, after the lenticule has been removed, an implant is placed in the cornea. The method ReLEx smile additionally makes it possible to use the pocket-like cutting geometry created as a result of the method to receive the implant and thereby offer a certain amount of mechanical stability. In any case, the known cutting geometry allows the inlay to substantially slip out of place after the operation, thereby disrupting the visual impression.